It is well known in the art that a frequent application of a conventional type of hydraulic vibration tester device is found in a component element fatigue test in reference to a sine wave form in a low frequency range due to the fact that a high output or a high amplitude may easily be produced of a low cost compared with that of electrically operated vibration testers.
However, the most popular servo valve is of a nozzle flapper type and also the most popular type of a hydraulic vibrating machine is one having this kind of servo valve. Thus, in case of this kind of vibrating machine, it is found that an upper limit of the working frequency is a low frequency of about 200 to 300 Hz due to structural restrictions of the nozzle flapper. As special testing equipment, a hydraulic vibrating machine having a direct drive type servo valve may also be applied in a frequency range of 500 to 650 Hz. However, this type of testing equipment has the disadvantage that the transmitted force is decreased in reverse proportion to the square of the number of vibrations, as shown in FIG. 1, when the resonance frequency f.sub.n (500 to 650 Hz) of the tester device is exceeded. The resonance frequency f.sub.n is thus the practical upper limit of the working frequency range of the tester device, resulting in that a conventional type of a hydraulic vibrating tester device may not be used in a higher frequency range higher than about 500 to 650 Hz.